This disclosure relates generally to a method and apparatus for improved display of digital mammographic images.
Digital mammographic images or mammograms are usually presented as gray scale images having individual pixels, with each pixel having a pixel value corresponding to a specific gray scale value. These gray scale values may lie within a range of values between a minimum value of, for example, 0 (black) and a maximum value of, for example, 225 (white). The edge length of a typical mammogram is approximately 2000 to 4000 pixels, and the dissolution of a typical mammogram is approximately 10 line pairs/mm and/or 0.1 mm/pixel.
A mammographic imaging system may be coupled to a workstation, for example, a PACS (Picture Archiving and Communication System) workstation, on which a mammogram may be viewed and reviewed by a physician or other medical professional. Mammography assigned PACS workstations usually have high resolution monitors, which are able to represent the high volume range and the comparatively high resolution of mammographic images.
Mammographic imaging systems generate raw mammograms containing measured data. These raw mammograms exhibit a global image characteristics with a comparatively high contrast in a boundary region of the measured object (i.e., the boundary region of the breast) and a relatively low contrast inside the measured object (i.e., the inside the breast). Conventional PACS workstations typically include tools for selecting parts of the whole gray scale level range and displaying these parts with maximum contrast through window level settings. Gray scale level ranges outside of the selected gray scale level window are mapped to the smallest or highest possible gray scale level, which means that information contained in these outside ranges is no longer displayed. Alternatively, nonlinear transfer functions represented through so called lookup tables may be applied to the raw mammogram modifying the global image characteristics in order to achieve a better over-all-contrast. Since the available total range of gray scale levels is fixed, a contrast enhancement for a selected part of the gray scale level range leads to a decrease of contrast in other gray level ranges. Therefore, an optimal display of all gray scale levels of the mammogram with optimal contrast and sharpness cannot be achieved by applying window level settings and/or lookup tables.
In the case of a mammogram a fundamental problem results in the fact that it is difficult to visualize structures within the breast. At the same time, structures within the background do not have to be visualized. The actual interesting structures are represented within the breast by pixel values, which do not use the entire range of values available, but use values within a comparatively small range. Therefore, the contrast between the pixels of the actual interesting structures is thus comparatively small.
Well known level and window functions use a global adjustment of the contrast between the pixels for contrast optimization, as for example the contrast between pixels with pixel values in a certain range of values is increased (the range of values is spread), all pixels with pixel values outside of this range of values however on the minimum or maximum pixel value is at the same time are set In this way, the contrast for certain structures, for example within the represented close gland fabric of a breast may be optimized, while the contrast within other ranges, received at the same time, are not optimal and may be within set ranges, so that the information is not represented into individual ranges any longer.
Therefore, there is a need for a method and apparatus for an intuitive way for a physician or other medical professional to locally optimize the contrast of a mammographic image in a particular portion of the mammographic image.